What is BMI?

Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI is a fairly reliable indicator of body fatness for most people.

BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

How is BMI calculated and interpreted?

Calculation of BMI

BMI is calculated the same way for both adults and children. The INTERPRETATION of that BMI is different for adults and children. First, how BMI is calculated:

Measurement Units
Formula and Calculation
Kilograms and meters (or centimeters) Formula: weight (kg) / [height (m)]2

With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.

Example: Weight = 68 kg, Height = 165 cm (1.65 m)

Calculation: 68 ÷ (1.65)2 = 24.98

Pounds and inches Formula: weight (lb) / [height (in)]2 x 703

Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.

Example: Weight = 150 lbs, Height = 5’5″ (65″)

Calculation: [150 ÷ (65)2] x 703 = 24.96

 

Interpretation of BMI for adults

For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women. For children and teens, on the other hand, the interpretation of BMI is both age- and sex-specific.

For more information about interpretation for children and teens, visit Child and Teen BMI Calculator.

The standard weight status categories associated with BMI ranges for adults are shown in the following table.

BMI
Weight Status
Below 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and Above Obese

For example, here are the weight ranges, the corresponding BMI ranges, and the weight status categories for a sample height.

Height
Weight Range
BMI
Weight Status
5′ 9″ 124 lbs or less Below 18.5 Underweight
125 lbs to 168 lbs 18.5 to 24.9 Normal
169 lbs to 202 lbs 25.0 to 29.9 Overweight
203 lbs or more 30 or higher Obese

Here is a chart to calculate your BMI

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